Because you don't want to disassemble the grill unit, I have a suggestion. I purchased some 2" felt buffing pads from Harbor Freight and used them with my air angle dye grinder. Used Mothers metal polish. I restored all of the windshield and rear window trim with this system. The trim looks brand new. I realize that the window trim is stainless and the grill surround is aluminum but I suspect with the anodizing gone you should get good results. This assumes you have a compressor for the dye grinder. I have not tried it with an electric drill which spins more slowly but I am sure it would be better than hand rubbing. Pads will build up a residue as you work but there should be more than enough in the kit to finish the grill shell. Here is a link to the pads on Harbor Freight's web site:
http://www.harborfreight.com/2-inch-...kit-95993.html